Utilisation des franges d'interference en lumiere diffuse pour l'etude de l'etat de surface d'un diffuseur

A diffuser, illuminated successively by light of two neighbouring wavelengths, produces on a photographic plate placed in a parallel plane two intensity distributions which are homothetic except for certain decorrelation terms. This homothecy (scale variation) can be compensated by a longitudinal displacement of the photographic plate between the two exposures and consequently, the decorrelation depends only on the structure of the diffuser. Under these conditions, if the photographic plate is given an additional displacement in its own plane between the two exposures, the contrast of Young's fringes obtained in the Fourier plane characterises the roughness of the diffuser.     

Modification de l'absorption hertzenne d'un gaz sous l'action d'un champ infrarouge non resonant

With non-resonant infrared laser radiation, a frequency shift of the microwave absorption line of ammonia is observed. The experimental data are in good agreement with the theory of the Stark effect in a rapidly-varying field.     

Etude theorique d'un mesureur absolu des flux laser continus base sur les echanges d'impulsion

We present in this paper a theoretical study of an absolute cw laser power meter based on the mechanical effects of the light (momentum transfer from a light beam to a target). We show that an appropriate geometry of the device leads to a result which ignores the target and beam characteristics and depends only on the incident flux value.     

Reconstitution d'un profil d'eclairement echantillonne par une ligne de micro-photodiodes

We have studied experimentally the spatial photosensitivity distribution of a self-scanned photodiode array. Using this data, we have calculated a reconstruction function which restores exactly the profile of a light distribution sampled by an array infinite extent under the Nyquist conditions. We briefly discuss the noise limitations and the truncation effects introduced by the finite number of diodes of a real array.     

Determination des angles d'obliquite d'un cristal liquide en phase nematique au voisinage d'une surface

Using several laser sources the dispersion of the quadrupole nonlinear tensor d⁽²⁾(CaCO₃) has been determined in the ultraviolet and visible range 265 – 592 nm. The measured dependence is in a good agreement with the predicted dispersion d⁽²⁾(CaCO₃) ~ λ^-1.     

Calcul de la fonction correlation de phonon pour la diffraction d'une particule par un solide

A method of calculating expressions of the type $\text{<T exp[?i}\text{k}{}_1\text{u}{}_{\ln }\text{(t}{}_1\text{)] ... exp [?i}\text{k}{}_{\mathrm{n}}\text{u}{}_{\ln }\text{(t}{}_{\mathrm{n}}\text{>}$ which is simpler than that based on Wick's theorem is proposed. Expressions of the above type are widely used in studying the effects of temperature in electron and neutron diffraction.     

Transmission d'images et d'hologrammes par une nappe de fibres optiques au moyen d'un codage chromatique

A new method of addition of 2-D complex optical signals is proposed. The addition is performed by suitably matched spatial filtering. For that purpose the effect of compacting of periodic objects images is employed.     

Mesure de l'impulsion echangee au cours de l'interaction onde evanescente-atome

In vacuo, during an interaction between a moving atom and a surface wave of frequency v, the exchanged momentum is greater than hv/c. First we show, using a semi-classical treatment, that this momentum is ?k_x in agreement with De Broglie's relation p = ?k, but unlike the usual notion of wave momentum attached to the Poynting vector. We present experimental methods to measure this momentum and we give results for two atom speeds.     

Réalisation d'un simulateur de corps noir pour l'étalonnage absolu des détecteureurs de flux lumineux

For the purpose of absolute calibration of luminous flux detectors against a grey thermopile, a primary standard has been built which is a blackbody simulator having a conial cavity observed along a parallel to its axis.     

Application effective de l'interferometrie holographique par double exposition a l'etude des deformations de ceramiques,dues a l'impact d'un projectile

This paper reports upon experiments made in the field of high speed holography by double exposure. These experiments allowed to establish at different moments, the map of deformations of the surface of a ceramic plate undergoing the action of a projectile impact.     

Determination de la longueur de covariance d'une surface rugueuse par l'etude de la diffusion residuelle a l'infini

We propose a simple method for directly measuring the correlation length of a slightly rough surface by using the residual scattered light. As in a previous work about strong diffusors, we use the experimental results to discuss the validity of Beckmann's theory on surface scattering, now in the case of weak diffusors.     

Etude spectroscopique de l'effet d'anode

Spectral lines of LiI emitted by an anodic plasma, produced during electrolysis of a KCl-LiCl mixture, have been observed. This paper deals with diagnostic studies of this plasma and is based on a comparison of observed line profiles for LiI(2P-3D), (2P-4S) and (2P-4D, 4F) with calculated values derived from the Griem-Baranger impact theory. We have found, from the ensemble of the results, that the electron density in the plasma center is N_e(0) ? 1·8×10¹⁷ cm^-3, the electron temperature is T_e(0) ? 9×10³ °K, and the plasma thickness is l ? 200 μ.     

Sur la diffraction d'une onde plane electromagnetique par un reseau metallique

This paper deals with the diffraction of a plane electromagnetic wave by metallic gratings. Some calculations have already been achieved on an UNIVAC 1110 computer in both ultraviolet and visible regions.     

Etude spectroscopique d'un jet de plasma d'argon hors d'equilibre thermodynamique local

We have studied the properties of an argon plasmajet seeded with a few percent of hydrogen. At atmospheric pressure, significant deviations from local thermodynamic equilibrium (L.T.E.) are shown. The plasma parameters (electrondensity N_e, temperature T) have been determined from the broadening and the absolute intensity of hydrogen lines. The transition probabilities and the broadening parameters (width and shift) of some AI lines between 4000 and 6000 Å have been measured.     

Autocorrelation d'un diffuseur depolarisant

The autocorrelation of a depolarizing diffuser illuminated successively by two linearly polarized beams of light is proportional to the cosine of the angle between the directions of polarization. The speckle pattern exhibits the same properties of correlation.     

Utilisation de l'heterodynage optique pour des mesures locales de la vitesse de phase d'ondes elastiques

A new optical method for measuring the acoustical wavelengths with a great accuracy has been investigated. An acousto-optical interaction is performed and the acoustical frequency range is such that the diffraction take place in “Bragg regime”. The phase modulation of the scattered laser beam is visualized by means of an optical heterodyning. When the location of the acousto-optical interaction is linearly displaced, the detected beating signal supplies a local measurement (10 μ) of the acoustical wavelength.     

Accroissement d'energie interne et de densite d'energie interne d'un milieu dielectrique polarise

For an isotropic dielectric medium, having an arbitrary shape and a stationary polarization, the polarization-induced increase of internal energy of the dielectric only is reexamined from Güntelberg's thermodynamic point of view. The value obtained for this increase is quite different from what was previously admitted, even in the case of dielectrics with simple shapes. The new value is in better agreement with earlier results. It is furthermore well in accord with the exact macroscopic relation between the internal energy and a density of internal energy, a relation which is more intricate than the simple relation of integration largely accepted up to now.     

Sur l'entropie de vibration des défauts dans l'approximation d'einstein

The vibration entropies of bulk or defect atoms of a crystal (vacancies, clean or rough surfaces) are given, in general, with a good precision in the Einstein approximation. In this approximation we compare the Montroll-Potts model to a model with central potentials between first nearest neighbours and to a model with central and second nearest neighbours and also angular interactions in order to show that, for sites having unsymmetrical neighborhood, one has in general to define different Einstein frequencies for different normal modes of vibration. The results in the last model show also the importance of angular forces and central forces between second neighbors. Finally the precision of the calculation of the surface entropy is i if one does an Einstein-like approximation on a dynamical matrix written for each k∥.     

Procede experimental de restitution de la partie imaginaire de l'amplitude complexe d'un objet de phase

An experimental process is described, capable of restoring the imaginary part of the complex amplitude of a phase object. It is based on a combination of phase-modulation interferometry and scanning the object by a flying-spot method. This experiment proves that it is possible to obtain the sign of the phase, and so the direction of surface relief.     

Nouvelles evidences experimentales dans l'interpretation du spectre de diffusion Rayleigh d'un cristal plastique de succinonitrile

We have verified on 3 important points the validity of the application of the hydrodynamic theory previously used to interpret the spectra of the Rayleigh scattering in a plastic crystal of succinonitrile. (1) The half-width Γ is varying as the square of the transfer wave vector q in a domain much larger than the one studied previously (Γ = Dq²). (2) Measurement of the coefficient of thermal diffusivity and comparison with D. (3) Measurement of the Rayleigh factor and comparison with the theory.